In medical surgery, automated or semi-automated techniques are getting increasingly common for cutting human or animal tissue. For example, WO 2011/035792 A1 describes a computer assisted and robot guided laser osteotome medical device. This device uses a robot arm guided laser, such as an Er:YAG laser, to cut human or animal hard tissue, such as bone tissue, by photoablating the tissue along a predefined osteotomic line. Such a device can, e.g., allow for precise cutting of bone tissue which preciseness is increasingly demanded in many applications, for example, in the field of reconstructive surgery or the like.
Automated cutting tools or devices such as the device mentioned hereinbefore usually have tracking means by which position and orientation of target tissue and the laser head can be tracked. For example, today optical or magnetic tracking systems are used, which usually monitor the body part or tissue and the laser head, and detect deviations in position and/or orientation. For tracking, the body part and laser head are usually provided with appropriate marker shields or means recognizable by the tracking system.
Whereas classic cutting tools, such as saws and the like, have difficulty performing cutting geometries which are more complex than straight or slightly bent cuts, ablating bone with a laser allows for applying comparably complex cutting geometries. For example, with the device mentioned above, saw-tooth, dove-tail, and other specific cutting geometries with an associated functionality are possible. Cutting bones in such comparably complex geometries allows for a variety of new applications, e.g., in the field of reconstructive surgery and bone shaping.
However, the cutting widths possible with today's laser systems, which usually are in a range of 200 μm and smaller, pose high demands on the precision of the applied cuts. Minor geometrical errors in an applied cut can prevent proper application such as reassembling of cut bone pieces, for example, after shifting them with regard to each other. If, for example, the body part of the patient moves during the cutting process or when the cutting process is interrupted by, e.g., the surgeon, laser guiding means such as the robot has to be able to automatically reposition with high accuracy to continue the cutting process.
Today's optical or magnetic tracking systems are, however, not accurate enough as their best precision is usually in the range of 200 μm, which is not suitable compared to what, e.g., is required for robot-guided laser osteotomy. In addition thereto, today's robots or similar means are capable of moving with a preciseness up to about 200 μm. Thus, the overall preciseness of robot and tracking system are together not appropriate for many applications.
Therefore, there is a need for an automatic or a semi-automatic surgery apparatus and method allowing application of cuts in human or animal hard tissue with comparably complex geometries at a comparably high precision.
In particular, there is a need for providing a sufficiently precise movement of a cutting instrument, such as a laser beam, in relation to a tissue to cut such that comparably complex cutting geometries are applicable.